In the Tl1-yPbyCaSr2Cu2O7 system, monophasic superconducting compositions are formed in the range 0.25 < y < 0.60 and the minimum Pb content required to stabilize the tetragonal 1122 phase is about 25%. Maximum Tc is found when y = 0.5, at which composition the hole concentration is optimal. Metallic compositions of Tl1−yPbyCaSr2Cu2O7 (y = 0.25) and Tl0.75Pb0.25Y1−xCaxSr2Cu2O7 (0.80 ⩽ X ⩽ 1.0) become superconducting on decreasing the oxygen content by vacuum annealing.
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